Method of reference signaling resource allocation for control channel transmission in wireless communication system

ABSTRACT

In legacy systems such as 3 rd  Generation Partnership Project (3GPP) releases 8 to 10, the control channel is transmitted using the first few Orthogonal Frequency Division Multiplexing (OFDM) symbols in a subframe. The limited control channel capacity will impact the system performance in future releases as more and more User Equipments (UEs) will be scheduled in a subframe with technologies such as MulitUser-Multiple Input Multiple Output (MU-MIMO) and Coordinated Multipoint (CoMP) transmission being enhanced or introduced. A new Enhanced Control CHannel (E-CCH) is necessary to be designed, which will use the resource in the Physical Downlink Shared CHannel (PDSCH) in the legacy systems. The E-CCH will support UE-specific DeModulation Reference Signal (DMRS) based transmission and receiving. However, the configuration of DMRS for E-CCH is necessary to be known to UE in prior. This invention discloses multiple methods in which DMRS is configured for E-CCHs and respective eNB and UE behaviors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior application Ser.No. 13/676,643, filed on Nov. 14, 2012, which claimed the benefit under35 U.S.C. §119(e) of a U.S. Provisional application filed on Nov. 14,2011 in the U.S. Patent and Trademark Office and assigned Ser. No.61/559,263, and a U.S. Provisional application filed on Nov. 21, 2011 inthe U.S. Patent and Trademark Office and assigned Ser. No. 61/562,074,the entire disclosure of each of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless cellular communicationsystem with at least one enhanced Node B (eNB) and at least one UserEquipment (UE). More particularly, the present invention relates to awireless communication system in which multiple physical antennas arerepresented by logical antenna ports in reference signals.

Throughout the following description of exemplary embodiments of thepresent invention, the 3^(rd) Generation Partnership Project (3GPP) LongTerm Evolution (LTE) Release 8-10 is regarded as a legacy system whereasthe in-development Release 11 and future releases are considered to besystems in which exemplary embodiments of the present invention can beimplemented. However, this is not intended to be a limitation of theinvention or its application and it is to be understood that the currentinvention can also be applied to other cellular systems whereappropriate.

2. Description of the Related Art

Generally, mobile communication systems have been developed to provide avoice communication service to users on the move. As time hasprogressed, mobile communication systems have evolved to support datacommunication services as well as standard voice communication services,and can now also support high speed data communication services.However, there is a need for more sophisticated mobile communicationsystems to mitigate resource shortages and to meet the high-speedservice requirements of users.

The LTE system is a next generation broadband communication technologydeveloped by the 3GPP in order to meet such requirements. The LTE systemis a technology for realizing high-speed packet-based communication atup to 100 Mbps. To achieve these requirements, discussions are beingheld on various aspects. For example, discussions are being heldregarding one scheme for reducing the number of nodes located in acommunication path by simplifying a configuration of the network, andanother scheme for maximally approximating wireless protocols towireless channels.

In the aforementioned LTE wireless communication system, at least twokinds of reference signals are defined.

The first kind of reference signal is referred to as a Common ReferenceSignal (CRS). CRS is cell specific, and all the UEs connecting to theeNB can use CRS for demodulation when CRS-based transmission isconfigured.

The second kind of reference signal is referred to as a DeModulationReference Signal (DMRS). DMRS is UE specific. That is, the UE will usethe DMRS within its allocated resources for demodulation of the saidallocation resources, where the DMRS and the data are precoded with thesame weights among antenna ports.

The control channel is usually transmitted in the beginning of asub-frame in order that the UE can efficiently acquire the schedulinginformation as quickly as possible. Considering the 3GPP LTE as anexample, the Physical Downlink Control CHannel (PDCCH) is configured tobe transmitted in the first one to four Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in a sub-frame.

FIG. 1 illustrates a subframe structure with 2-OFDM-symbol PDCCH andDMRS with ports 7˜14 configured according to the related art.

Referring to FIG. 1, the ports 7˜10 use a spreading factor of 2 tomultiplex two DMRS ports on two consecutive Resource Elements (REs) inthe time domain. Ports 11˜14 use the same resource as ports 7˜10 but usea spreading factor of 4 for to multiplex 4 DMRS ports on the fourconsecutive REs in a subcarrier.

To increase the capacity of the legacy PDCCH, the Enhanced ControlCHannel (E-CCH) is proposed to be allocated in the legacy PhysicalDownlink Scheduling CHannel (PDSCH) region. DMRS based transmissionshould be supported for E-CCH since E-CCH should work for those specialMulticast-Broadcast Single Frequency Network (MBSFN) subframes where CRSis absent. The E-CCH corresponds to Enhanced Physical Downlink ControlCHannel (E-PDCCH) described in LTE standard specification.

In the legacy system, DMRS is used for decoding of PDSCH. Thecharacteristics of the DMRS configurations, including the number of DMRSports and scrambling sequence ID, are indicated to the UE using DownlinkControl Information (DCI) in the PDCCH. However, if DMRS is used forE-CCH transmission, the DMRS configuration cannot be previouslyindicated by the control channel itself. Thus, a predefinedconfiguration or implicit indication should be enabled for the UE toobtain DMRS configurations.

There are basically two kinds of E-CCH structures.

-   -   Interleaved mode: an Enhanced Control Channel Element (E-CCE)        contains REs distributed in multiple Resource Blocks (RBs);    -   Localized mode: an E-CCE contains REs within one RB

Exemplary embodiments of the present invention focus on the case ofE-CCH with localized E-CCE distribution.

FIG. 2 illustrates an E-CCE localized structure in an RB, where 4 E-CCEsare allocated in one Physical Resource Block (PRB) in a subframe,according to the related art.

Referring to FIG. 2, a logical E-CCE can contain a set of eitherconsecutive or distributed physical REs in the RB. FIG. 2 alsoillustrates a physical structure, where an E-CCE consists of REs inthree distributed subcarriers, according to the related art. Theallocated REs for E-CCH exclude those REs allocated for legacy PDCCH,and any type of reference signals when configured.

Therefore, a need exists for methods of allocation of DMRS resources andimplicit indication of DMRS configuration for E-CCH transmission.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide methods to implicitly indicate the DeModulationReference Signal (DMRS) configuration to a User Equipment (UE) forEnhanced Control CHannel (E-CCH) transmission.

In accordance with an aspect of the present invention, a system isprovided. The system allocates a DMRS resource according to the resourcesize allocated for E-CCH transmission. For example, when multiple E-CCHsare multiplexed in one Resource Block (RB), four DMRS ports should beconfigured. And when only one E-CCH is scheduled in one RB, the systemshould only configure two DMRS ports for resource saving. After the DMRSports are configured, the system can either perform rate matching orpuncturing around the DMRS Resource Elements (REs) when mapping theE-CCH payload to REs, according to particular exemplary embodiments.

In accordance with an aspect of the present invention, a method forreceiving a control channel by a user equipment in a wirelesscommunication system is provided. The method comprises receivingconfiguration information of the control channel from a base station,identifying an aggregation level of the control channel transmitted fromthe base station, determining a size of a resource allocated to thecontrol channel depending on the identified aggregation level, anddecoding subframes received from the base station depending on resultsof the determination.

In accordance with another aspect of the present invention, a UE forreceiving a control channel from a base station in a wirelesscommunication system is provided. The UE comprises a communication unitconfigured to transmit or receive a signal to or from the base station,and a control unit configured to receive configuration information aboutthe control channel from the base station, to identify an aggregationlevel of the control channel, to determine a size of a resourceallocated to the control channel depending on the identified aggregationlevel, and to decode subframes received from the base station dependingon results of the determination.

In accordance with yet another aspect of the present invention, a methodfor transmitting a control channel by a base station in a wirelesscommunication system of is provided. The method includes transmittingconfiguration information of the control channel for the user equipmentto the user equipment, generating a control channel that includescontrol information related to the user equipment scheduled in anysubframe, identifying an aggregation level of the generated controlchannel and determining resources for DMRS depending on the identifiedaggregation level, and transmitting the control channel through thedetermined resources to the user equipment.

In accordance with still another aspect of the present invention, a basestation for transmitting a control channel in a wireless communicationsystem is provided. The Base Station includes a communication unitconfigured to transmit or receive a signal to or from user equipment,and a control unit configured to transmit configuration information ofthe control channel for the user equipment to the user equipment, togenerate the control channel that includes control information relatedto the user equipment scheduled in any subframe, to identify anaggregation level of the generated control channel, to determineresources for DMRS depending on the identified aggregation level, and totransmit the control channel through the determined resources to theuser equipment.

According to an exemplary implementation of the present invention, thebase station can implicitly indicate the DMRS configuration to the UE,and the UE can determine a size and region of the control channelallocated to itself without separate signaling. Accordingly, it ispossible for the wireless communication system to use limited resourcesefficiently and reduce the load.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a sub-frame structure with 2-OFDM-symbol PhysicalDownlink Control Channel (PDCCH) and DeModulation Reference Signal(DMRS) with ports 7˜14 configured according to the related art.

FIG. 2 is an illustration of Enhanced Control Channel Element (E-CCE)localized structure in a Resource Block (RB), where 4 E-CCEs areallocated in one Physical Resource Block (PRB) in a subframe, accordingto the related art.

FIG. 3 is an illustration of the possible multiplexing of multipleEnhanced Control CHannels (E-CCHs) in an RB according to an exemplaryembodiment of the present invention.

FIG. 4 is an illustration of DMRS configuration and E-CCE mapping ofmethod 0 according to an exemplary embodiment of the present invention.

FIG. 5 is an illustration of DMRS configuration and E-CCE mapping ofmethod 1 according to an exemplary embodiment of the present invention.

FIG. 6 is an illustration of DMRS configuration and E-CCE mapping ofmethod 2 according to an exemplary embodiment of the present invention.

FIG. 7 is an illustration of DMRS configuration and E-CCE mapping ofmethod 3 according to an exemplary embodiment of the present invention.

FIGS. 8A and 8B are illustrations of an enhanced Node B (eNB) and a UE'scorresponding procedures of method 2 according to exemplary embodimentsof the present invention.

FIGS. 9A and 9B are illustrations of an eNB's and a UE's correspondingprocedures according to method 2 according to an exemplary embodiment ofthe present invention.

FIGS. 10A and 10B are illustrations of an eNB's and a UE's correspondingprocedures of method 3 according to an exemplary embodiment of thepresent invention.

FIG. 11 is a block diagram illustrating an inner structure of a userequipment in accordance with an exemplary embodiment of the presentinvention.

FIG. 12 is a block diagram illustrating an inner structure of an eNB inaccordance with an exemplary embodiment of the present invention.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Exemplary embodiments of the present invention focus on a scenario thata DeModulation Reference Signal (DMRS) is used for Enhanced ControlCHannel (E-CCH) transmission. E-CCH is transmitted on n number ofE-CCHs. Namely, an Enhanced Control Channel Element (E-CCE) is atransmission unit of E-CCH. Here, n may have one value of 1, 2, 4 and 8according to exemplary embodiments of the present invention.

A 4 E-CCE per Resource Block (RB) structure was illustrated in FIG. 2,where an RB consists of 4 logical E-CCEs. The E-CCE is the basic unitfor E-CCH transmission. An E-CCH can use 1/2/4/8 E-CCEs fortransmission. When aggregating E-CCEs in localized mode, the systemaggregates those consecutive E-CCEs in the configured RB resources, sothat the resulting E-CCH also consists of consecutive resources. Whenthere are four E-CCEs in an RB, the E-CCH with 1, 2, 4, 8 aggregationlevels will occupy ¼, ½, 1, 2 RBs respectively.

FIG. 3 is an illustration of the possible multiplexing of multipleE-CCHs in an RB according to an exemplary embodiment of the presentinvention.

Referring to FIG. 3, it is noted that an E-CCH with aggregation levelone can start from any E-CCE index i, an E-CCH with aggregation leveltwo can only start from any E-CCE index i with imod2=0, an E-CCH withaggregation level four can only start from any E-CCE index i withimod4=0, and an E-CCH with aggregation level eight can only start fromany E-CCE index i with imod8=0. For simplicity, it is assumed that theE-CCH transmission is restricted with rank 1, and one DMRS port isnecessary for each of the E-CCHs. In alternative exemplaryimplementations, it is also possible to higher rank transmission, e.g.,rank 2, wherein two DMRS ports are necessary for each of the E-CCHs.

When an RB is multiplexed with four E-CCHs with aggregation level one,four DMRS ports are needed for each of the E-CCH. When an RB ismultiplexed with three E-CCHs with aggregation levels one and two, threeDMRS ports are needed for each of the E-CCH. When an RB is multiplexedwith two E-CCHs with aggregation level two, two DMRS ports are neededfor each of the E-CCH. When an RB is multiplexed with one E-CCH withaggregation level four or eight, one DMRS port is needed for the E-CCH.

It is further assumed that a User Equipment (UE) will receive indicationas to which DMRS port is allocated for a certain E-CCH or search space.This indication could be explicitly configured by higher layerconfiguration, or implicitly indicated with other conditions, e.g., theDMRS port is related to the E-CCE index, or the starting E-CCE index ofan E-CCH. Because the detailed indication method is beyond the scope ofthe present invention, it will not be treated further.

Exemplary Method 0: Maximum DMRS Port Configuration

FIG. 4 is an illustration of DMRS configuration and E-CCE mapping ofmethod 0 according to an exemplary embodiment of the present invention.

Referring to FIG. 4, in method 0, the system always configures 4 DMRSports for any aggregation level of E-CCH. Although for aggregations fourand eight, only one DMRS port is necessary, and the Resource Elements(REs) for DMRS ports 9˜10 are still configured. When allocating E-CCHpayload to the REs, those DMRS REs for ports 9˜10 are left unused, orthese REs are used for other purposes. At the UE side, the UE willalways assume all the RBs carrying E-CCHs are configured with 4 DMRSports, regardless of their actual aggregation levels. No E-CCH symbolsare mapped onto those DMRS REs, regardless if they are used for DMRS,blank, or used for other purposes.

A benefit of method 0 is that it is simple for UE operation. However, itmay have unused/wasted REs when two or less DMRS is needed.

Exemplary Method 1: DMRS Port Configurations Depending on AggregationLevels

In an exemplary embodiment, the system will configure 4 DMRS portresources for those RBs with at least one E-CCH of aggregation level oneor two, and configure 2 DMRS port resources for those RBs withaggregation level four or eight. Note that for the case when two E-CCHswith aggregation level two are multiplexed in one RB, only two DMRSports are needed. However, when a UE detects an E-CCH with aggregationlevel two, it will have no knowledge if the remaining two E-CCEs in thesame RB will be allocated as one E-CCH of aggregation level two, or twoE-CCHs of aggregation level one. Thus, for the case of E-CCH ofaggregation level two, 4 DMRS port REs are assumed.

At the UE side, the UE will first generate search spaces for eachaggregation level. A search space is defined as a set of resources wherean E-CCH for the particular UE can be transmitted. The amount of searchspace is limited for simplicity. The UE will try to decode each searchspace of every aggregation level. If the Cyclic Redundancy Check (CRC)of the decoded sequence passed, the UE will assume the decoding of theE-CCH is successful.

Based on the above-discussed description, an exemplary embodiment of thepresent invention will be now described.

First, the following description assumes that in any RB, four kinds ofsignals, E-CCH (or the Physical Downlink Scheduling CHannel (PDSCH), thesame will apply hereinafter) of one UE, DMRS of one UE, E-CCH of anotherUE, and DMRS of another UE, are transmitted.

FIG. 5 is an illustration of DMRS configuration and E-CCE mapping ofmethod 1 according to an exemplary embodiment of the present invention.

Referring to FIG. 5, resource or resources for one or more UEs may beallocated to one resource block, and resource allocating information istransmitted to the UE from the eNB through the E-CCH.

In this case, if the E-CCH with at least one of aggregation levels 1 and2 is transmitted, the first UE, as illustrated in FIG. 3, recognizesthat resource allocating information about another UE is contained in acorresponding resource block that transmits the E-CCH. Thus, if the DMRSfor the first UE is transmitted through the DMRS ports 7˜8 asillustrated in FIG. 5, the first UE assumes that the DMRS of the otherUE is transmitted through the DMRS ports 9˜10 illustrated in FIG. 5.This is because, as described above, if the aggregation level of theE-CCH is at least one of the aggregation levels 1 and 2, a resource ofany UE other than the first UE may be allocated, and accordingly, theDMRS for the first UE and the other UE should be transmitted in acorresponding resource block.

As a consequence, the first UE assumes that if the aggregation level isat least one of aggregation levels 1 and 2, E-CCH is not transmitted atthe region corresponding to DMRS ports 9˜10. Namely, the first UEassumes that the E-CCH is transmitted on the rest of resources exceptresources corresponding to the DMRS ports 7˜10.

Meanwhile, in the case of transmitting the E-CCH with the aggregationlevel 4 or 8, the first UE recognizes that, as illustrated in FIG. 3,the resource allocation information and data of the first UE itself, notof the other UE, are transmitted on the corresponding resource block.Thus, if the DMRS of the first UE is transmitted on the DMRS ports 7˜8as illustrated in FIG. 5, the first UE assumes that the E-CCH of thefirst UE, not the DMRS of the other UE, is transmitted on the regioncorresponding to the DMRS ports 9˜10. This is because, as describedabove, in case where the aggregation level of E-CCH is either 4 or 8,only a resource of the first UE can be allocated in the correspondingresource block.

Consequentially, the first UE assumes that if the aggregation level iseither 4 or 8, the E-CCH is transmitted on the region corresponding tothe DMRS ports 9˜10. Namely, the first UE assumes that the E-CCH istransmitted on the rest of resources except the region corresponding tothe DMRS ports 7˜8.

As discussed above, according to an exemplary embodiment of the presentinvention, the UE determines the size of resources depending on theaggregation level of the E-CCH, and performs the decoding process usingthe determined size of resources.

FIGS. 8A and 8B are illustrations of an eNB's and a UE's correspondingprocedures of method 2 according to exemplary embodiments of the presentinvention.

Referring to FIG. 8A, an eNB first configures the UE for its E-CCHconfiguration (configuration related to E-CCH region) in step S810. Inan exemplary implementation, the configuration can be part of higherlayer Radio Resource Control (RRC) signaling.

In step S820, the eNB schedules the UE for each subframe. In anexemplary implementation, if a UE is scheduled, the eNB continues toschedule its E-CCH resources if configured. The E-CCH schedulingincludes E-CCH aggregation level, and E-CCEs to carry the E-CCH.

In step S830, if a UE's E-CCH has been configured as localized modebased on DMRS, the eNB will configure the DMRS port according to theaggregation level of the E-CCH. If the E-CCH is of aggregation level oneor two, the eNB will configure four DMRS port resources (i.e., port7˜10) in the RB which carries the E-CCH. If the E-CCH is of aggregationlevel four or eight, the eNB will configure two DMRS port resources(i.e., port 7˜8) in the RB(s) which carries the E-CCH.

In step S840, the eNB continues to map E-CCH payload symbols toallocated E-CCEs. Rate matching is performed around the configured DMRSREs, i.e., the eNB will allocate E-CCH symbol to next available RE byskipping the DMRS REs.

In step S850, the eNB transmits the scheduled E-CCH in the subframe.

A corresponding exemplary procedure at the UE is illustrated in FIG. 8B.

In step S860, the UE first receives the configuration of its E-CCH fromthe eNB.

In step S870, when the UE is configured with localized mode E-CCH basedon DMRS, for each subframe received, the UE first generates the searchspaces for each aggregation level.

In step S880, the UE starts blind decoding for each search space. Whenthe search space is of aggregation level one or two, the UE will assume4 DMRS port resources are configured and no E-CCH is mapped onto thoseDMRS REs. When the search space is of aggregation level four or eight,the UE will assume 2 DMRS port resources are configured and no E-CCH ismapped onto those DMRS REs.

The UE decides if an E-CCH is successfully received or not after blindlydecoding all the search spaces. If an E-CCH is received, the UE willperform corresponding procedures.

Exemplary Method 2: Minimal DMRS Port Configurations

FIG. 6 is an illustration of DMRS configuration and E-CCE mapping ofmethod 2 according to an exemplary embodiment of the present invention.

In another exemplary embodiment, the system will configure only thenecessary number of DMRS resources for E-CCH. For the example in FIG. 3,4 DMRS port resources are configured for case (a) and (b), and 2 DMRSport resources are configured for case (c) and (d). In cases when 4 DMRSport resources are configured, for the E-CCHs port 7 or 8 are assignedfor demodulation, the eNB will assume rate matching only for two DMRSports (ports 7˜8), and perform symbol puncturing for DMRS REs foranother two ports (ports 9˜10), as shown in FIG. 6 for the E-CCHs port 9or 10 are assigned for demodulation, rate matching is performed for DMRSREs for ports 9˜10. In cases when 2 DMRS port resources are configured,the eNB behaves the same as what is described in method 1, and performsrate matching for the DMRS REs. Here, puncturing the E-CCH symbol meansan E-CCH symbol is assign to the DMRS port 9-10 REs, but replaced by theDMRS symbol for actual transmission.

At the UE side, the UE will assume only 2 DMRS port resources areconfigured for E-CCH search spaces assigned with ports 7˜8 regardless oftheir aggregation level and assume 4 DMRS port resources are configuredfor E-CCH search spaces assigned with ports 9˜10. When an E-CCH symbolis actually punctured by a DMRS RE, the UE is unaware of the puncturingand will take the DMRS RE as a received E-CCH symbol for decoding.

FIGS. 9A and 9B are illustrations of an eNB's and a UE's correspondingprocedures according to method 2 according to an exemplary embodiment ofthe present invention.

Referring to FIG. 9A, an eNB first configures the UE for its E-CCHconfiguration in step 910. In an exemplary implementation, theconfiguration can be part of higher layer RRC signaling.

In step 920, the eNB schedules the UE for each subframe.

If a UE is scheduled, the eNB continues to schedule its E-CCH resourcesif configured. The E-CCH scheduling includes E-CCH aggregation level,and E-CCEs to carry the E-CCH.

In step 930, if the UE's E-CCH has been configured as a localized modebased on DMRS, the eNB will configure a DMRS port of each E-CCH RBaccording to the number of E-CCHs multiplexed in the RB. If more thantwo E-CCHs are multiplexed, the eNB will configure four DMRS portresources (i.e., ports 7˜10) in the RB which carries the E-CCH.Otherwise, the eNB will configure two DMRS port resources (i.e., ports7˜8) in the RB(s) which carries the E-CCH.

In step 940, the eNB continues to map E-CCH payload symbols to allocatedE-CCEs. For an E-CCH assigned with port 7 or 8, rate matching isperformed around the configured DMRS REs for ports 7˜8. If ports 9˜10are also configured, the eNB will puncture corresponding E-CCH symbolswhich are mapped to the DMRS ports 9˜10 REs. For an E-CCH assigned withport 9 or 10, rate matching is performed around the configured DMRS REsfor ports 7˜10.

In step 950, the eNB transmits the scheduled E-CCH in the subframe.

A corresponding exemplary procedure at the UE is illustrated in FIG. 9B.

In step 960, the UE first receives the configuration of its E-CCH fromthe eNB.

In step 970, when the UE is configured with localized mode E-CCH basedon DMRS, for each subframe received, the UE first generates the searchspaces for each aggregation level.

In step 980, the UE starts blind decoding for each search space. If thesearch space is assigned with port 7 or 8 for demodulation, the UE willassume 2 DMRS port resources are configured and no E-CCH is mapped ontoDMRS ports 7-8 REs. The UE will also assume E-CCH symbols aretransmitted on DMRS ports 9˜10 REs. If the search space is assigned withport 9 or 10 for demodulation, the UE will assume 4 DMRS port resourcesare configured and no E-CCH is mapped onto DMRS ports 7-10 REs. The UEwill also assume no E-CCH symbols are transmitted on DMRS port 9˜10 REs.

The UE decides if an E-CCH is successfully received or not after blindlydecoding all the search spaces. If an E-CCH is received, the UE willperform corresponding procedures.

Exemplary Method 3: DMRS Port Spreading Factor Depending on AggregationLevels

FIG. 7 is an illustration of DMRS configuration and E-CCE mapping ofmethod 3 according to an exemplary embodiment of the present invention.

Referring to FIG. 7, the system will configure 2 DMRS port (ports 7˜8)resources for those RBs with E-CCH of aggregation level four or eight,and configure additional DMRS port (ports 11˜12) resources for those RBswith at least one E-CCH of aggregation level one or two. Note that DMRSports 11-12 use the same DMRS REs as ports 7˜8. When four ports 7,8,11and 12 are configured, the spreading factor of four should be assumedfor DMRS based channel estimation.

For the eNB, it will always configure DMRS port resources for ports 7˜8.When more than two DMRS ports are necessary, the eNB will transmitadditional DMRS using ports 11 and 12. Rate matching is performed aroundthe configured DMRS REs for E-CCH payload mapping.

At the UE side, the UE will first generate search spaces for eachaggregation level. When the aggregation level of a search space is oneor two, the UE will assume DMRS with a spreading factor of four forchannel estimation of the RB where the search space is located. When theaggregation level of a search space is four or eight, the UE will assumeDMRS with a spreading factor of two for channel estimation of the RBwhere the search space is located.

FIGS. 10A and 10B are illustrations of an eNB's and a UE's correspondingprocedures of method 3 according to an exemplary embodiment of thepresent invention.

Referring to FIG. 10A, an eNB first configures the UE for its E-CCHconfiguration in step 1010. In an exemplary implementation, theconfiguration can be part of higher layer RRC signaling.

In step 1020, the eNB schedules the UE for each subframe.

If a UE is scheduled, the eNB continues to schedule its E-CCH resourcesif configured. The E-CCH scheduling includes E-CCH aggregation level,and E-CCEs to carry the E-CCH.

In step 1030, if a UE's E-CCH has been configured as a localized modebased on DMRS, the eNB will configure a DMRS port according to theaggregation level of the E-CCH. If more than two E-CCHs are multiplexed,the eNB will configure four DMRS port resources (i.e., port 7, 8, 11,12) in the RB which carries the E-CCH when necessary. Otherwise, the eNBwill configure two DMRS port resources (i.e., port 78) in the RB(s)which carries the E-CCH.

In step 1040, the eNB continues to map E-CCH payload symbols toallocated E-CCEs. Rate matching is performed around the configured DMRSREs, i.e., the eNB will allocate E-CCH symbol to next available RE byskipping the DMRS REs.

In step 1050, the eNB transmits the scheduled E-CCH in the subframe.

A corresponding exemplary procedure at the UE is illustrated in FIG.10B.

In step 1060, the UE first receives the configuration of its E-CCH fromeNB.

In step 1070, when the UE is configured with localized mode E-CCH basedon DMRS, for each subframe received, the UE first generates the searchspaces for each aggregation level.

In step 1080, the UE starts blind decoding for each search space. Whenthe search space is of aggregation level one or two, the UE will assumeDMRS port 7, 8, 11, 12 resources are configured with spreading factorfour. When the search space is of aggregation level four or eight, theUE will assume DMRS port 7, 8 resources are configured with spreadingfactor two. The UE will use a corresponding spreading factor for DMRSchannel estimation. The UE assumes rate matching for E-CCH for the DMRSREs, and no E-CCH is mapped onto those DMRS REs.

The UE decides if an E-CCH is successfully received or not after blindlydecoding all the search spaces. If an E-CCH is received, the UE willperform corresponding procedures.

FIG. 11 is a block diagram illustrating an inner structure of a UE inaccordance with an exemplary embodiment of the present invention.

Referring to FIG. 11, the UE may include a communication unit 1110(e.g., a transceiver), a storage unit 1120, and a control unit 1130.

The communication unit 1110 may transmit or receive a signal to or fromthe eNB. The signal transmitted or received to or from the eNB mayinclude a data channel, a control channel, and the like.

The storage unit 1120 may store programs required for operation of theUE. Particularly, the storage unit 1120 may store programs that performa series of processes for determining the size of resources allocated tothe control channel depending on an aggregation level of the controlchannel.

The control unit 1130 controls signal flows between internal blocks ofthe UE to perform operations of the UE.

More particularly, the control unit 1130 controls to receiveconfiguration information related to the control channel from the eNB,and to identify an aggregation level of the control channel. The controlunit 1130 controls to determine the size of a resource that is allocatedto the control channel depending on the identified aggregation level andto decode subframes received from the base station depending on resultsof the determination.

More particularly, if the identified aggregation level is at least oneof 1 and 2, the control unit 1130 determines that resources of thecontrol channel are the rest of resources except resources for DMRSrelated to all UEs capable of being scheduled among resource blocks.Additionally, if the aggregation level is either 4 or 8, the controlunit 1130 determines that resources of the control channel are the restof resources except resources for DMRS related to the UE.

Here, the control channel may be Enhanced-Physical Downlink ControlCHannel (E-PDCCH).

FIG. 12 is a block diagram illustrating an inner structure of an eNB inaccordance with an embodiment of the present invention.

Referring to FIG. 12, the eNB may include a communication unit 1210(e.g., a transceiver), a storage unit 1220, and a control unit 1230.

The communication unit 1210 may transmit or receive a signal to or fromthe UE. The signal transmitted or received to or from the UE may includea data channel or a control channel.

The storage unit 1220 may store programs required for operation of theeNB. More particularly, the storage unit 1220 may store programs thatperform a series of processes for determining resources for DMRSdepending on an aggregation level of control channels that will betransmitted to the UE.

The control unit 1230 controls signal flows between internal blocks ofthe eNB to perform operations of the eNB.

More particularly, the control unit 1230 controls to transmitconfiguration information of the control channel for the UE to the UE,and to generate a control channel that includes control informationrelated to the UE scheduled in any subframe. And the control unit 1230controls to identify the aggregation level of the generated controlchannel, to determine resources for a DMRS depending on the identifiedaggregation level, and to transmit the control channel through thedetermined resources to the UE.

More particularly, if the identified aggregation level is at least oneof 1 and 2, the control unit 1230 determines that resources of thecontrol channel are the rest of resources except resources for DMRSrelated to all UEs capable of being scheduled among resource blocks. Ifthe aggregation level is either 4 or 8, the control unit 1230 determinesthat resources of the control channel are the rest of resources exceptresources for DMRS related to the UE.

Here, the control channel may be E-PDCCH.

According to the above-discussed exemplary embodiments of the presentinvention, the eNB can implicitly indicate the DMRS configuration to theUE, and the UE can determine a size and a region of the control channelallocated to itself without separate signaling. Accordingly, it ispossible for the wireless communication system to use limited resourcesefficiently and reduce the load.

While this invention has been particularly shown and described withreference to an exemplary embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims and their equivalents.

What is claimed is:
 1. A method for monitoring a control channel by auser equipment in a wireless communication system, the methodcomprising: receiving configuration information on the control channelfrom a base station; identifying a subframe in which the user equipmentmonitors the control channel based on the configuration information;determining a demodulation reference signal (DMRS) port index formonitoring the control channel depending on an aggregation level of thecontrol channel; and monitoring the control channel in the subframeusing the determined the DMRS port index, wherein at least two DMRS portindices are used for monitoring the control channel if the aggregationlevel of the control channel is
 2. 2. The method of claim 1, wherein atleast four DMRS port indices are used for monitoring the control channelif the aggregation level is
 1. 3. The method of claim 1, wherein atleast one DMRS port is used for monitoring the control channel if theaggregation level is either 4 or
 8. 4. The method of claim 1, whereinthe control channel is an enhanced-physical downlink control channel(E-PDCCH).
 5. The method of claim 1, wherein the configurationinformation on the control channel includes information on a controlchannel region.
 6. The method of claim 1, wherein the determiningfurther comprises: determining the DMRS port index for monitoring thecontrol channel depending on the aggregation level of the controlchannel if the control channel is configured for localized transmission.7. A user equipment for monitoring a control channel from a base stationin a wireless communication system, the user equipment comprising: acommunication unit configured to transmit or receive a signal to or fromthe base station; and a control unit configured to: receiveconfiguration information on the control channel from the base station,identify a subframe in which the user equipment monitors the controlchannel based on the configuration information, determine a demodulationreference signal (DMRS) port index for monitoring the control channeldepending on an identified aggregation level of the control channel, andmonitor the control channel in the subframe using the determined theDMRS port index, wherein at least two DMRS port indices are used formonitoring the control channel if the aggregation level is
 2. 8. Theuser equipment of claim 7, wherein at least four DMRS port indices areused for monitoring the control channel if the aggregation level is 1.9. The user equipment of claim 7, wherein at least one DMRS port is usedfor monitoring the control channel if the aggregation level is either 4or
 8. 10. The user equipment of claim 7, wherein the control channel isan enhanced-physical downlink control channel (E-PDCCH).
 11. The userequipment of claim 7, wherein the configuration information on thecontrol channel includes information on a control channel region. 12.The user equipment of claim 7, wherein the controller is furtherconfigured to determine the DMRS port index for monitoring the controlchannel depending on the aggregation level of the control channel if thecontrol channel is configured for localized transmission.
 13. A methodfor transmitting a control channel by a base station in a wirelesscommunication system, the method comprising: transmitting configurationinformation including information associated with a subframe in which auser equipment (UE) monitors the control channel to the UE; andtransmitting the control channel in the subframe to the UE, the controlchannel being associated with a demodulation reference signal (DMRS)port index depending on an aggregation level of the control channel,wherein at least two DMRS port indices are used for monitoring thecontrol channel if the aggregation level is
 2. 14. The method of claim13, wherein at least four DMRS port indices are used for monitoring thecontrol channel if the aggregation level is
 1. 15. The method of claim13, wherein at least one DMRS port is used for monitoring the controlchannel if the aggregation level is either 4 or
 8. 16. The method ofclaim 13, wherein the control channel is an enhanced-physical downlinkcontrol channel (E-PDCCH).
 17. The method of claim 13, wherein theconfiguration information includes information on a control channelregion.
 18. The method of claim 13, wherein the control channel isassociated with a DMRS port index depending on the aggregation level ofthe control channel if the control channel is configured for localizedtransmission.
 19. A base station for transmitting a control channel in awireless communication system, the base station comprising: acommunication unit configured to transmit or receive a signal to or fromuser equipment; and a control unit configured to: transmit configurationinformation including information associated with a subframe in which auser equipment (UE) monitors the control channel to the UE, and transmitthe control channel in the subframe, being associated with ademodulation reference signal (DMRS) port index depending on anidentified aggregation level of the control channel, to the UE, whereinat least two DMRS port indices are used for monitoring the controlchannel if the aggregation level is
 2. 20. The base station of claim 19,wherein at least four DMRS port indices are used for monitoring thecontrol channel if the aggregation level is
 1. 21. The base station ofclaim 19, wherein at least one DMRS port is used for monitoring thecontrol channel if the aggregation level is either 4 or
 8. 22. The basestation of claim 19, wherein the control channel is an enhanced-physicaldownlink control channel (E-PDCCH).
 23. The base station of claim 19,wherein the configuration information includes information on a controlchannel region.
 24. The base station of claim 19, wherein the controlchannel is associated with a DMRS port index depending on theaggregation level of the control channel if the control channel isconfigured for localized transmission.